1. Field of the Invention
The present invention relates to a system and method for generating a flexible time slot in an internal voice mail system.
2. Description of the Related Art
A private branch exchange (PBX) is a telephone exchange system for all employees to share a specific number of external telephone lines used in a company and for automatically connecting telephones of internal users connected to extensions. And, a keyphone system is switch and connection equipment that can accept one or more office lines and one or more extensions, and can switch and connect a channel between an office line and an extension using a telephone.
In particular, types of circuit switching include space-division circuit switching used in an analog switch, and time-division circuit switching used in a digital switch. In addition, there is a method of switching between a space-division speech path of which a switch is set up into a matrix to select a channel, and a time-division speech path that transmits a time-division-multiplexed input signal to an output line when a time position is changed.
The time-division speech path method uses a plurality of channels through one transmission line. Such a method dividing time and thereby multiplexing one transmission line is referred to as time-division multiplexing (TDM), the transmission line is referred to as a highway, and a time position of each channel in the highway is referred to as a time slot.
Therefore, when a signal of each channel is transmitted to the highway in digital signal format, time-division-multiplexed digital information divided into time slots for each channel is decoded in an output side highway to obtain an analog signal and thereby carry out communication. A time-division switching method is performed according to this principle.
A pulse code modulation (PCM) highway is used in an internal voice mail system, etc., of a PBX or a keyphone system described above, and a time slot assignment signal used for enabling the PCM highway is fixed.
Since the time slot assignment signal is fixed by integrated circuits (ICs) (U14 and U8), there is insufficient ability to cope with variation in a number of ports of a voice mail system or a low-capacity keyphone system.
For example, even when a transmit start of transfer (TSX) signal of a two- or four-channel unit is needed, an eight-channel unit is used, wastefully. In addition, when eight channels or more are needed, an additional IC must be used for every eight channels, as described above.
Therefore, the conventional art does not possess flexible functionality and has limitations with respect to cost, packaging degree, and so on, when the number of channels increases.